In this paper, intense up- and down-conversion luminescence were successfully achieved in well designed and synthesized core-shell structured NaLuF4:Gd/Yb/Er@NaLuF4:Yb@NaLuF4:Nd/Yb@NaLuF4 nanoparticles (NPs) simultaneously under 808 nm continuous-wave laser excitation. The morphologies, luminescent properties and energy transfer mechanism of the nanoparticles were studied in detail. By employing this design, multimodal imaging performance including near-infrared down-conversion optical imaging and X-ray computed tomography (CT) imaging were realized in one kind of NPs. Furthermore, the 808 nm excited optical temperature sensing property of the synthesized NPs was realized in a wide temperature range by monitoring the intensities of up- and down-conversion luminescence. This study provides a novel platform based on lanthanide fluoride nanoparticles for multifunctional imaging and temperature sensing in one system.